“Long, Long Ago” which preemed Tuesday on cabler American Movie Classics, will air again at 1 p.m. Saturday. The one-hour docu features recollections of 26 senior citizens on their early moviegoing experiences. It was produced and directed by Ray Farkas; exec producer was Lewis A. Bogach.* Librarian of Congress James Billington has named 20 members to the National Film Registry Board. Appointees include MPAA prexy Jack Valenti, National Assn. of Theater Owners’ Ted Pedas, Screen Actors Guild’s Roddy McDowall and National Society Film Critics’ David Kehr.